The present invention relates to an ignition control device as well as to a corresponding ignition control method.
Although applicable to any ignition control devices, the present invention as well as the problem underlying in are discussed with reference to an engine control device on board a motor vehicle.
Ignition control devices for controlling ignition events for coil ignition systems and devices essentially have two control functions, the controlling of a desired ignition energy over the duration of operation, i.e., the charging period of the coil, as well as the angle-correct controlling of an ignition pulse beyond the switch-off time point, i.e., the end of the coil charging.
In the case of coil ignition systems, the ignition energy that is measured over a charging time of the coil is of varying durations, in accordance with the electrical system voltage applied to the electrical switching circuit of the coil as well as with the time constants of the electrical switching circuit.
Usually, the specific setpoint values are stored as a characteristics field in the control unit, as a function of the speed and possible further engine parameters.
When a speed dynamic arises, the setpoint values, xe2x80x9ccharging timexe2x80x9d and xe2x80x9cignition angle,xe2x80x9d generate a conflict in goals. The angular position at the commencement of the charging phase, i.e., the initial dwell angle, must be selected such that, after the termination of the charging time, the ignition angle is achieved. This means that at the time point of the calculation of the ignition events, the time-angle curve of the crankshaft motion must already be known.
In the event of an extreme speed dynamic and low-frequency speed readout, especially during engine startup, a non-negligible estimation error of this time-angle curve arises in conventional ignition control devices.
For generating angular signals, conventional control units have at their disposal an angle transmitter wheel, which supplies to the ignition control device pulses that are equidistant in their angle. However, for reasons relating to the computing run-time, the calculation of the ignition events in most ignition control device architectures only takes place segment by segment, one segment being the angular interval of 720xc2x0 of the crankshaft divided by the number of cylinders, i.e., in a four-cylinder engine, for example, 180xc2x0. Therefore, although the angular positions of the ignition events, ascertained in the calculation, are measured with sufficient precision by the angle transmitter wheel and by the timer/counter circuits customary in ignition control devices, nevertheless the calculation itself proceeds on the basis of a measured speed, which, given the speed dynamic at the site of the ignition, is no longer valid.
To explain the problem, FIG. 1 depicts a schematic representation of the ignition sequence in a four-cylinder internal combustion engine.
In FIG. 2, crankshaft angle KW is plotted in xc2x0 on the X axis and ignition curve ZZ is plotted on the Y axis, the ignition curve having the sequence . . . -2-1-3-4-2- . . . The complete cycle amounts to 720xc2x0 KW corresponding to a cycle time tZYK. One segment amounts to 720xc2x0 KW/4=180xc2x0 corresponding to one segment time tSEG.
FIG. 3 depicts a schematic representation of the ignition control functional sequences in the segment of the first cylinder of the four-cylinder internal combustion engine with respect to the driving of coil current IZ.
At 0xc2x0, speed N is measured and immediately thereafter charging time tL and ignition angle wZ (approximately equal to the final dwell angle) are derived from a characteristics field B.
Subsequently, the initial dwell or charging angle wLB is determined from the equation
xe2x80x83WLB=WZxe2x88x92tLxc2x7xcfx89
assuming a uniform motion, xcfx89 being the angular velocity corresponding to speed N. For reasons having to do with the computing run-time, this temporal and angular position of the ignition events is calculated only once every ignition interval.
In the case of the charging-time output mode, angle wLB is measured by a counter C1 starting from 0xc2x0, using crankshaft sensor signal KWS, and when angle WLB is reached, the driver stage of the coil is triggered. Charging-time duration tL is controlled using a timer and, after the elapsing of charging-time duration tL, the triggering is interrupted.
In the case of the ignition-angle output mode, angle wLB is measured by a counter C1 starting from 0xc2x0, using crankshaft sensor signal KWS, and when angle WLB is reached, the driver stage of the coil is triggered. Using a further counter C2, starting from 0xc2x0, angle wZ is measured using crankshaft sensor signal KWS, and when angle wZ is reached, the triggering is interrupted.
Since the erroneous calculation of the speed curve, e.g., in the case of engine startup, is not negligible, a prioritization of the control aims, charging time and ignition angle, is usually undertaken in ignition control devices. If the emphasis is on the exact output of the charging timexe2x80x94so-called charging-time output modexe2x80x94using the timer/counter circuit, then in response to the startup acceleration (speed increase), a retard shift of the ignition angle results. On the other hand, if the ignition angle is precisely read outxe2x80x94so-called ignition-angle output modexe2x80x94, then the charging time diminishes in response to the startup dynamic and thus the energy in the coil as well, which can lead to misfiring.
Therefore, usually the output method, i.e., charging-time output or ignition-angle output, is permanently preestablished as a function of the characteristics of the targeted system, or a switchover of the output method takes place in response to a threshold speed. In this context, a charging-time output is usual during startup, and a switchover to ignition-angle output is usual beginning from a threshold speed, at which the speed readout reaches such high frequency levels that the dynamic error is negligible, beginning from which, on the other hand, the sensitivity of the torque over the ignition angle falls off steeply.
An automatic selection of the output method via a generally valid calculation specification, which the output method independently determines during the calculation time from the current physical conditions, is therefore desirable.
In contrast to the known solutions, the ignition control device according to the present invention and the corresponding ignition control method have the advantage that a selection of the ignition method is carried out that corresponds to the current physical conditions of the ignition control device. In other words, an expedient model-specific representation is provided, within the ignition control device, of the physical correlations of significance for the coil ignition. In this manner, the operating mode most favorable for the ignition control device and for the relevant engine can be selected, without expensive applications.
This is advantageous in the case of ignition control devices that do not permit a clear prioritization of the output methods, charging-time output and ignition-angle output. The use of ignition units, i.e., coils and ignition devices, having moderate charging times and their installation on the cylinder head, which under certain circumstances is hot, results here in greater degrees of freedom. In addition, the present invention makes it easier to apply the ignition control device because the mode selection is automatically determined from the current physical conditions. Accommodation to the requirements of various areas of use is therefore significantly simpler.
The idea underlying the present invention is that an estimate of an error of the ignition angle in the charging-time output mode and/or an error of the charging time in the ignition-angle output mode is carried out on the basis of a possible speed change after the recording time point. Based on the estimated error, e.g., when a threshold value is exceeded, a determination of the ignition control mode takes place from the modes, ignition-angle output and charging-time output, for the ignition segment.
Preferably, the ignition angle error in the time output mode is estimated and, on the basis of this estimation, it is decided whether the ignition-angle output or charging-time output mode is selected. In other words, the ignition control device independently decides whether the supposed output error is still tolerable.
According to one preferred refinement, the error estimating device is configured such that it estimates a shift of the ignition angle in the charging-time output mode, and the ignition control mode evaluation device selects the ignition-angle output mode if the estimated shift exceeds a preestablished threshold value.
According to a further preferred refinement, the error estimating device has a speed measurement error estimating device for estimating the speed measurement error taking into account the speed and/or the change over time in the speed; a weighting device for weighting the estimated speed measurement error on the basis of the determined charging time; and a correction device for ascertaining a correction corresponding to a possible speed change between the measuring time point and the initial charging time point, corresponding to the initial charging angle.
According to a further preferred refinement, the error estimating device has a temperature measuring device for measuring the engine temperature, and a characteristic curve device for indicating an estimated value for the shift, on the basis of the measured engine temperature.